In the current mobile unit communication system, mainly, communication services are provided by base stations each of which forms a macrocell that is a wide communication area. In a description below, a base station that forms a macrocell is sometimes referred to as a “macro base station”.
However, an area, such as the inside of a building, in which a radio wave transmitted from a macro base station is hardly reached, sometimes becomes an out-of-communication-service area or a non-detection area, such as an area in which communication is unstable. Accordingly, measures are taken to relieve this non-detection area such that a small-size base station with small transmission electrical power is arranged in a macrocell and, by using this small-size base station, a femtocell whose communication area is smaller than that of the macrocell is formed in the macrocell. In a description below, a small-size base station that forms a femtocell is sometimes referred to as a “femto base station”.
Because a femto base station is usually arranged inside of a building, the femto base station is connected to a mobile telecommunication network via a public line, such as a broadband line arranged inside of the building. Furthermore, the femto base station provides the same communication service as that provided by the macro base station with respect to a communication terminal that is used by a user. Because the femto base station is connected to a mobile telecommunication network by using a public line, no dedicated line is needed to arrange the femto base station. Accordingly, for mobile unit telecommunication carriers, due to the arrangement of femto base stations, it is possible to take measures against non-detection areas at low cost, which is an advantage. Furthermore, due to the arrangement of the femto base station in a macrocell, it is possible to accommodate a communication terminal, which is conventionally accommodated in a macro base station, in the femto base station. Consequently, for mobile unit telecommunications carriers, due to the arrangement of the femto base station, an advantage is provided in that the communication resources in a macrocell can be efficiently used. Furthermore, due to the arrangement of the base station inside of a building, for a user of a communication terminal, an advantage is provided in that the state of a radio wave is improved and high-quality and large-volume communication is possible.
In recent years, with the development of high-performance communication terminals represented by smart phones, because data communication traffics are dramatically increased, it is difficult, only for macrocells, to satisfy demands of users who use high-quality communication terminals. Accordingly, in recent years, the femto base stations having various advantages are actively installed.
Related-art examples are described, for example, in Japanese Laid-open Patent Publication No. 2010-166272, Japanese Laid-open Patent Publication No. 2010-056881 and Japanese Laid-open Patent Publication No. 2011-250263.
Because femto base stations are often arranged in a macrocell as the measurements against a non-detection area in the macrocell, femtocells are often used in a manner such that the femtocells overlap with macrocells. Furthermore, in case of a power failure of a main power supply, a standby power supply functioning as an emergency power supply is connected to a typical macro base station. Thus, even if a power failure occurs in the main power supply, the macro base station can continue a communication service by switching the power supply from the main power supply to the standby power supply.
In contrast, because a typical femto base station does not include a standby power supply in case of a power failure, if a supply of electrical power from the main power supply to the femto base station is stopped due to the occurrence of a power failure or the like, the typical femto base station is not able to continue the communication service. Due to a stop of the communication service of the femto base station, a plurality of communication terminals accommodated in a femto base station simultaneously sends a location registration request to a macro base station. Consequently, in a macrocell, due to a stop of the communication service of the femto base station, congestion of communication data sometimes occurs. If congestion of the communication data occurs in a macrocell, a communication delay may sometimes occur in the communication of the communication terminals that are originally accommodated in a macrocell. Furthermore, if a core network located in a level higher than that of the macrocell detects congestion in the macrocell and thus performs call regulation on the entirety of the macrocell, the call regulation is also performed on the communication terminals that are originally accommodated in the macrocell. Consequently, a stop of the communication service of the femto base station adversely affect, such as a communication delay, call regulation, or the like, the communication terminals that are originally accommodated in the macrocell.